Plasma flame generator



March 22, 1966 MANABU YAMAMOTQ 3,242,308

PLASMA FLAME GENERATOR Filed March '7, 1963 J 2/ 7 a; 07 n/ m /M 3 6 United States Patent Oflice 3,242,308 Patented Mar. 22, 1966 3,242,303 PLASMA FLAME GENERATOR Manabu Yamamoto, Odawara-shi, Japan, assignor to Kabushiki Kaisha Hitachi Seisakusho, Tokyo-t0, Japan, a joint-stock company Filed Mar. 7, 1963, Ser. No. 263,581 Claims priority, application Japan, Mar. 14, 1962, 37/9,242 4 Claims. (Cl. 219-123) This invention relates to improvements in plasma flame generators.

In general, plasma flame generators, because of the necessity to prevent destructive consumption of their electrodes, have been designed to accomplish direct-current arc discharge within an inactive gas such as argon or nitrogen. However, in certain cases such as, for example, when such plasma flame generators are to be utilized as light sources for spectral analysis, there arises the necessity of introducing into the plasma also substances which have the possibility of eroding the electrodes upon contact therewith. In such a case, therefore, it is necessary to prevent, positively, the sample materials from contacting the electrode foot points at high temperature and, at the same time, to prevent irregular shifting of the positions of the foot points of the electrodes accomplishing electrical discharge. The electrode foot point herein designates a portion on the electrode surface where the arc root is contacted. If the electrode foot points shift irregularly, the discharge will become unstable, the emission intensity of the analyzed sample will fluctuate, and the precision of the spectral analysis will be lowered. The prevention of such an irregular shifting of the electrode foot points is of great importance, not only in the case of plasma flame generators used as spectral analysis light sources,

but also in the case of all such generators of this type generally used for a Wide range of uses.

In view of the foregoing consideration, it is an object of the present invention to provide a new and improved plasma flame generator which is capable of generating a stable, easily controlled plasma flame, and the electrodes of which have a long serviceable life.

The nature, principle, and details of the invention, as well as the manner in which the foregoing object and other objects and advantages may best be achieved will be best understood by reference to the following detailed description of a preferred embodiment of the invention, when read in conjunction with the accompanying drawing, which is an elevational view, in vertical section, showing the essential parts of the embodiment.

Referring to the drawing, the generator embodying this invention is composed, essentially, of a cylindrical electrode 1 made of a non-magnetic, electrically conducting material, a cylindrical nozzle 2 on the vertical centerline of the electrode 1 at its upper part, a conical passage part 3 with its narrow upper end connected to the lower end of the nozzle 2 and its wide end connected to means (not shown) for supplying a stream 7 of an inactive gas such as argon or nitrogen, a bar electrode 4 having a pointed tip which is disposed in the conical passage part 3 so as to confront the electrode 1 and is supported in an electrically insulated manner, a gas feeding path 5 from the outer side surface of the electrode 1 to the conical passage part 3, and a small bar magnet 6 with one magnetic pole thereof at the inner surface of the conical passage part 3.

By the above-described constructional arrangement, an arc column 9 is generated with the tip of the bar electrode 4 and the inner surface of the conical passage part 3 of the cylindrical electrode 1 as electrode foot points when electric power is supplied to the electrodes 4 and 1 by suitable means (not shown). A discharge plasma is thus created and, being pushed by the stream 7 of an inactive gas, is forced through the nozzle 2 to become a plasma jet 10, which is thus ejected outward.

Since the electrode foot points of the arc discharge during this operation are exposed to the high speed gas flow 7, there is the possibility of the foot point of the inner surface of the conical part 3 being disturbed and causing the arc column to become unstable. However, this possibility is eliminated by the magnet 6, the magnetic field of which is utilized to hold the arc root on the conical electrode surface 3 at a single point 11. This holding force is represented by Flemings left hand law; and, in the case illustrated in the drawing, in addition to the position indicated therein, it is possible for the electrode foot point 11 to exist in a stable state also on the opposite side, that is, on the symmetrically opposite position relative to the surface of the drawing paper. The actual position is determined by the polarity of the magnet.

When the electrode foot point is fixed at a definite point in this manner, the generation of the plasma flame is extremely stable, and the fluctuation in light intensity is also very slight. In order to utilize this generator as a spectral analysis light source, a gas flow 8 containing the sample to be analyzed is supplied through the gasfeeding path 5. Samples in powder or mist form are convenient for supplying together with a gas. Even if a sample is an active material with the possibility of eroding the high-temperature electrode foot point, this spectral analysis sample will be swept by the gas flow 7 and be discharged through the nozzle 2, being excited and caused to luminesce at an intermediate point within the plasma 10. Accordingly, there is absolutely no risk of erosion of the electrode foot point.

Furthermore, when the flow rate of the inactive gas flow 7 increases, the electrode foot point 11 tends to be blown toward the nozzle 2, but since this tendency is suppressed by electromagnetic force, the gas flow rate has the effect also of suppressing fluctuations in the arc path length and in the voltage.

Moreover, the number of magnets need not be limited to one. By disposing in a geometrical arrangement a suitable number of magnetic poles in accordance with the required magnetic field strength and distribution, it is possible to fix the electrode foot point at a desired point according to the purpose. For example, it has been found as a result of experiments that, for spectral analysis, the disposition of the position of the electrode foot point 11 as near as possible to the sample feeding aperture and, moreover, along the outer periphery of the said sample feeding aperture is of the greatest importance for improvement of sensitivity of analysis. In providing such disposition, however, it is important to make certain adjustments such as those of the fixed position of the foot point, the position and configuration of the sample feed ing aperture, and the gas flow rate so as to prevent the sample from contacting the electrode foot point.

It is a unique and advantageous feature of the generator of the present invention that extremely fine adjustments can readily be made through the configuration and arrangement of magnetic poles as described hereinabove. While, in the embodiment described above, the construction is that wherein a bar magnet is embedded within an electrode, one or more magnets may be arranged on the outside of a nozzle electrode in order to facilitate external adjustment. Furthermore, since variations in velocity of flow, temperature, length of flame, and other characteristics of the plasma ejected from the nozzle are produced by varying the intensity of the magnetic field, it is possible, by this measure, to control with ease the ejection of the plasma jet. Accordingly, modulation of the generated flame is also possible by impressing an alternating magnetic field.

In order to indicate still more fully the capability of the generator of the present invention to generate a stable plasma flame, the following example of its performance is presented. First, a fluctuation of the arc voltage of approximately percent was obtained in the generator with a construction without application of a magnetic field. It was easily observable by the naked eye that the fluctuation was caused by the shifting of the position of the electrode foot point. Then, when a magnetic field was impressed on the electrode, the fluctuation decreased to 2 percent, and the light intensity also became stable.

Thus, the plasma flame generator of the present invention is capable of maintaining a stable discharge and, at the same time, alfords control of the generated state of the plasma flame as desired in accordance with the necessity. Accordingly, the generator of this invention is particularly applicable as a light source for spectroscopic uses and can be used with great effectiveness also as a plasma flame generator for general use.

Although this invention has been described in conjunction with a particular embodiment thereof, it is to be understood that modifications and variations may be resorted to therein without departing from the spirit and scope of the invention, as those skilled in the art will readily understand, and such modifications and variations are to be considered to be within the purview and scope of the invention and appended claims.

What is claimed is:

1. A plasma flame generator comprising, in combination, a hollow electrode having a nozzle portion forming a gas flow path; a rod-shaped electrode, electrically insulated from said hollow electrode, disposed in spaced relation therewithin, opposite said nozzle portion; a sample inlet leading from the outside of said hollow electrode to the lower end of said nozzle portion; electrical means for generating an arc discharge between said electrodes; means for blowing an inert gas toward and through said nozzle portion from said rod-shaped electrode through a path formed between said electrodes; and means for impressing a magnetic flux in transverse direction of the arc to be generated in the gap formed between said electrodes, thereby fixing the foot point of said are at a definite position within said nozzle.

2. A plasma flame generator comprising, in combination, a first electrode, hollow on the inside, said hollow being divided into a truncated conical portion substantially in the lower half of said electrode and a cylindrical nozzle portion on top of said conical portio'n; a second, rod-shaped, electrode having a pointed tip, said second electrode being electrically insulated from said first electrode, and entering said conical portion from below, said pointed tip being disposed substantially in the upper third of the cone; a sample inlet leading from the side of said first electrode to the upper end of said conical portion; electrical means for generating an arc discharge between said electrodes; means for blowing an inert gas through said hollow from below through the path generated by said electrodes and through said nozzle portion; and means for impressing a magnetic flux in transverse direction of the are generated in the gap between said elec trodes, said magnetic flux holding the foot point of said are at a single point with said nozzle.

3. The generator as defined in claim 2, wherein said means for generating a magnetic flux consist of at least one magnet, one pole of which is disposed at the inner surface of the conical portion.

4. A plasma flame generator comprising, in combination, a first electrode, hollow on the inside, said hollow being divided into a truncated conical portion substantially in the lower half of said electrode and a cylindrical nozzle portion on top of said conical portion; a second, rod-shaped, electrode having a pointed tip, said second electrode being electrically insulated from said first electrode and entering said conical portion from below, said pointed tip being situated substantially in the upper third of the cone; a sample inlet leading from the side of said first electrode to the upper end of said conical portion; electrical means for generating an arc discharge between said electrodes; means for blowing an inert gas through said hollow from below through a path generated by said electrodes and through said nozzle portion; a magnet disposed substantially opposite said sample inlet at the upper part of said cone, one pole of said magnet being disposed on the inner surface of the cone; said magnet exerting a magnetic flux which holds the foot point of the are at a single point.

References Cited by the Examiner UNITED STATES PATENTS 2,475,183 7/1949 Gibson 219-123 2,862,099 11/1958 Gage.

2,972,695 2/1961 Wroe 219-123 X 3,102,946 9/1963 Fonberg 219-123 OTHER REFERENCES Holt: Method of Controlling Arc Blow, The Welding Engineer, April 1932, pp. 4446.

ARTHUR BARTIS, Acting Primary Examiner.

JOSEPH V. TRUHE, RICHARD M. WOOD, Examiners. 

1. A PLASMA FLAME GENERATOR COMPRISING, IN COMBINATION, A HOLLOW ELECTRODE HAVING A NOZZLE PORTION FORMING A GAS FLOW PATH; A ROD-SHAPED ELECTRODE, ELECTRICALLY INSULATED FROM SAID HOLLOW ELECTRODE, DISPOSED IN SPACED RELATION THEREWITH, OPPOSITE SAID NOZZLE PORTION; A SAMPLE INLET LEADING FROM THE OUTSIDE OF SAID HOLLOW ELECTRODE TO THE LOWER END OF SAID NOZZLE PORTION; ELECTRICAL MEANS FOR GENERATING AN ARC DISCHARGE BETWEEN SAID ELECTRODES; MEANS FOR BLOWING AN INERT GAS TOWARD AND THROUGH SAID NOZZLE PORTION FROM SAID ROD-SHAPED ELECTRODE THROUGH A PATH FORMED BETWEEN SAID ELECTRODES; AND MEANS FOR IMPRESSING A MAGNETIC FLUX IN TRANSVERSE DIRECTION OF THE ARC TO BE GENERATED IN THE GAP FORMED BETWEEN SAID ELECTRODES, THEREBY FIXING THE FOOT POINT OF SAID ARC AT A DEFINITE POSITION WITHIN SAID NOZZLE. 